Generally at the bottom of the plastic container, there will be a triangle-shaped plastic recycling logo symbol, the number is a few on behalf of several levels of material.
Level 1 material: PET - polyester. This material is mostly used for mineral water bottles and carbonated beverage bottles. This material has a heat-resistant temperature of 70 degrees Celsius, and is only suitable for warm and cold drinks, and the substances dissolved at high temperatures are harmful to the human body.
Level 2 material: HDPE - high density polyethylene. This material is mostly used to contain cleaning products, bath products, supermarkets and shopping malls in plastic bags, can withstand high temperatures. These containers are usually not good for cleaning, cleaning is not clean, it is best not to reuse.
Level 3 material: PVE - polyvinyl chloride. This material has been less used for packaging food products. One is the production process, not been fully polymerized monomolecular vinyl chloride, and the second is the plasticizer in the substance, are toxic and harmful substances.2017 World Health Organization, the International Agency for Research on Cancer announced that polyvinyl chloride in the list of class 3 carcinogens.
Class 4 material: LDPE - low density polyethylene. Cling film, plastic film, etc. are made of this material. If food is to be put in the microwave, the cling film should be removed first, otherwise the temperature at more than 110 degrees Celsius, the cling film will melt, leaving behind harmful substances that the human body can not decompose.
5 level material: PP - polypropylene. This material is mostly used in the manufacture of lunch boxes, its melting point of up to 130 ℃, can be put directly into the microwave oven to heat up food, clean and can be reused.
6 grade material: PS - polystyrene. This material is cold-resistant and heat-resistant, mostly used in the manufacture of instant noodle boxes, fast food boxes. This material is prone to releasing chemicals at high temperatures, so it's best not to use it to pack hot food.
7 level material: PC - polycarbonate. This is one of the most widely used materials, mostly used to make milk bottles, space cups and so on. It should be noted that PC in the case of high temperature, easy to release toxic substances bisphenol A, harmful to the human body. Do not heat it when using it and do not expose it to direct sunlight.
Often more than 4 plastic is called "food-grade", but through the above introduction, can also be seen, even if it is food-grade plastics, but also do not long in the high temperature state use.
The basic requirement for medical plastics is chemical stability and biosafety, because they are in contact with drugs or with the human body. Plastic materials in the constituent components can not precipitate into the drug or the human body, will not cause toxicity and damage to tissues and organs, the human body is non-toxic and harmless. In order to ensure the biosafety of medical plastics, the medical plastics usually sold on the market are certified and tested by medical authorities, and users are clearly informed of which grades are medical grade.
The following seven commonly used medical plastics:
One, polyvinyl chloride (PVC, Polyvinyl chloride)
PVC resin powder is white or light yellow powder, pure PVC is a random structure, hard and brittle, rarely used. According to different uses can be added to different additives, so that the PVC plastic parts show different physical and mechanical properties. In the PVC resin to add the appropriate amount of plasticizer, can be made into a variety of hard, soft and transparent products.
Hard PVC does not contain or contains a small amount of plasticizer, has a better tensile, flexural, compressive and impact resistance, can be used alone as a structural material. Soft PVC contains more plasticizers, its softness, elongation at break, cold resistance increased, but brittleness, hardness, tensile strength decreased. The density of pure PVC is 1.4g/cm3, and the density of PVC plastic parts with plasticizers and fillers etc. added is generally in the range of 1.15~2.00g/cm3.
According to incomplete estimates, about 25% of medical plastic products are PVC. mainly due to the resin's lower cost, wide range of applications, and its easy processing. PVC products for medical applications include: hemodialysis tubing, respiratory masks, oxygen tubing, and so on.
Two, polyethylene (PE, Polyethylene)
PE plastic is the plastics industry's largest production of varieties of milky white, tasteless, odorless and non-toxic glossy wax-like particles. Better performance, can be widely used in industry, agriculture, packaging and daily industry.
PE mainly includes low-density polyethylene (LDPE), high-density polyethylene (HDPE), as well as ultra-high molecular weight polyethylene (UHDPE) and other varieties. HDPE has fewer branched chains on the macromolecular chain, higher relative molecular mass, crystallinity, and density, greater hardness and strength, opacity is poor, higher melting point, commonly used in injection molded parts. lDPE comes with a number of branched chains, and thus has a smaller relative molecular mass, crystallinity and density. LDPE with many branched chains, thus smaller relative molecular mass, crystallinity and density is lower, with better flexibility, impact resistance and transparency, commonly used in blown film, is now widely used in PVC optional alternatives. It is also possible to mix HDPE and LDPE according to the performance requirements. UHDPE has high impact strength, low friction, stress crack resistance and good energy absorption properties, making it an ideal material for artificial hip, knee and shoulder connectors.
Three, polypropylene (PP, polypropylene)
PP colorless, odorless, non-toxic. Appearance like polyethylene, but more transparent and lighter than PE. PP is a thermoplastic with excellent performance, with a small specific gravity (0.9g/cm3), non-toxic, easy to process, impact resistance, flexural resistance and other advantages. It has a wide range of applications in daily life, including woven bags, films, crates, wire shielding materials, toys, car bumpers, fibers, washing machines and so on. Medical PP has high transparency, good barrier properties and radiation resistance, making it widely used in medical equipment and packaging industry. Non-PVC material with PP as the main body is a substitute for PVC material which is widely used nowadays.
Four, polystyrene (Polystyrene, PS) and K resin
PS is second only to polyvinyl chloride and polyethylene plastic varieties, usually as a single-component plastics processing and application, the main features are lightweight, transparent, easy to dye, molding and processing performance is good, so it is widely used in daily-use plastics, electrical parts, optical instruments and educational supplies. The texture is hard and brittle, with a high coefficient of thermal expansion, therefore, limiting its application in engineering. In recent decades, the development of modified polystyrene and styrene-based **** polymer, to a certain extent, to overcome the shortcomings of polystyrene. k resin is one of them.
K resin is made of styrene and butadiene **** polymer, it is an amorphous polymer, transparent, odorless, non-toxic, density of 1.01g/cm3 or so (lower than the PS, AS), impact resistance is higher than the PS, transparency (80 ~ 90%) good, the heat distortion temperature of 77 ° C, the K material contains butadiene component of the number of its hardness is also different, due to the K material, good fluidity, processing temperature is good. Because of the good fluidity of K material, processing temperature range is wider, so its processing performance is good.
The main uses in daily life include cups, lids, bottles, cosmetic packaging, hangers, toys, PVC substitute products, food packaging and pharmaceutical packaging supplies.
V, ABS, Acrylonitrile Butadiene Styrene **** polymer (Acrylonitrile Butadiene Styrene copolymers)
ABS has a certain degree of rigidity, hardness, impact resistance and chemical resistance, resistance to radiation and resistance to ethylene oxide sterilization. tools, roller clips, plastic needles, tool boxes, diagnostic devices and hearing aid shells, especially some of the shells of large medical equipment.
VI, polycarbonate (PC, Polycarbonate)
PC's typical characteristics are toughness, strength, rigidity and resistance to heat steam sterilization, these characteristics make PC preferred to become a hemodialysis filters, surgical tool handles and oxygen tanks (when in the surgical cardiac surgery, this instrument removes carbon dioxide in the blood and increases oxygen);
Medical applications of PC also include needleless injection systems, perfusion instruments, blood centrifuge bowls and pistons. Utilizing its high transparency properties, the usual myopia glasses are made of PC.
Seven, PTFE (polytetrafluoroethylene, Polytetrafluoro ethylene)
PTFE resin is a white powder, waxy appearance, smooth and non-stick, is the most important kind of plastic. PTFE has excellent performance, non-comparable to the general thermoplastics, and therefore has a "Plastic King PTFE has excellent performance, which is not comparable with general thermoplastics, so it is called "King of Plastics". Its coefficient of friction is the lowest among plastics, and it has good biocompatibility, so it can be made into artificial blood vessels and other directly implanted instruments in the human body.